Hydrogen release system

ABSTRACT

A system for discharging hydrogen from two or more hydrogen storage vessels ( 1 A,  1 B,  1 C) containing solid hydrogen storage material. The system includes at least one hydrogen supply line for connecting the hydrogen storage vessels to a hydrogen demand ( 3 ), an energy delivery system ( 6 A,  6 B,  6 C) to provide heat to the hydrogen storage material in each hydrogen storage vessel to desorb hydrogen from the solid hydrogen storage material, and one or more supply connection conduits ( 4 A,  4 B,  4 C) for connecting the supply line or lines to the hydrogen storage vessels ( 1 A,  1 B,  1 C). Each supply connection conduit has a backflow prevention device ( 5 A,  5 B,  5 C) to prevent hydrogen in the supply line from flowing back into the hydrogen storage vessels ( 1 A,  1 B,  1 C). Also disclosed is a system for delivering a supply of hydrogen to a hydrogen supply line including a control system ( 7 ) to determine the timing of activation of an energy delivery system based ( 6 A,  6 B,  6 C) on the hydrogen demand in the hydrogen supply line. The control system ( 7 ) activates the energy delivery system ( 6 A,  6 B,  6 C) in the next hydrogen storage unit to provide a sufficient period of time for the material in the next hydrogen storage vessel to heat to the temperature at which hydrogen is provided at the supply pressure for the hydrogen supply line.

FIELD OF THE INVENTION

This invention relates to a hydrogen release system and in particular ahydrogen release system including two or more hydrogen storage vesselsin which hydrogen is stored in the vessels within a hydrogen storagematerial.

BACKGROUND OF THE INVENTION

Hydrogen storage units utilising metal hydrides such as catalysed MgH₂require temperatures above 280° C. to effect a positive pressuredesorption. The heat loss from a heated well insulated solid statestorage cylinder with the dimensions of a commonly used G sizedcompressed gas cylinder can approximate 500 watts. Therefore, the heatloss from a heated 16 cylinder manifolded solid state pack canapproximate 8 kilowatts. This 8 kilowatts is additional to the energyrequired to break the MH-hydrogen bonds and affect the adsorption. Hencethe resulting thermal efficiency of such a system is extremely lowresulting in increased electricity usage and poor carbon footprint.

As each storage vessel requires significant heat input to desorbhydrogen, it is advantageous to heat one vessel at a time (1) to reducethe total heating power requirement at start-up or (2) enable thedesorption of hydrogen to occur at a much faster rate when a fixedamount of heating power is available. Hence, the applicant is pursuingthe concept of a manifolded storage system including a multiple numberof hydrogen storage vessels where only one cylinder is desorbing at atime.

Unlike a compressed gas storage unit, a solid state hydrogen storageunit containing hydrogen storage material empties under a constantpressure. In a compressed gas unit, the depth of discharge can beaccurately inferred from the remaining gas pressure in the cylinder. Incontrast, a solid state hydrogen storage unit will discharge from fullto over 90% empty at a constant equilibrium pressure determined by theoperating temperature. Once the volume of stored gas is too low tosupply the flow for the required demand, the pressure in the hydrogenstorage vessel will reduce quickly from the equilibrium point to zero.This is typically once the depth of discharge is beyond 90%.

Generally, when hydrogen is being desorbed from only a single vessel ata time, once the equilibrium pressure in that hydrogen storage vesselbegins to drop, it is too late to start heating up the next cylinder insequence as the time to bring the vessel to desorption pressure andtemperature far exceeds the remaining supply capacity of the currentnear empty vessel. In order to provide a constant supply of hydrogen tomeet a hydrogen demand, it is desirable that the next hydrogen storagevessel in sequence begins heating well before the constant equilibriumpressure begins to drop.

Additionally, once the active desorbing cylinder is empty, it isdesirable to cool down the cylinder to minimise heat loss. However,since the hydriding/dehydriding reaction is a reversible reaction, thereaction will reverse and the hydrogen storage material will absorbhydrogen once the temperature of the hydrogen storage material drops.FIG. 1 shows the absorption rate of MgH₂ as a function of temperaturefor a given pressure. For example, the plot of the absorption rateindicates that the reaction is in the desorption direction attemperatures above the equilibrium temperature. For temperatures belowthe equilibrium point the reaction is in the absorption direction.Therefore, if the cylinders are connected in parallel to a supplymanifold and the next cylinder in the sequence is now supplying hydrogenby being heated to above the equilibrium temperature, the previouscylinder will absorb all of this hydrogen as it cools down below theequilibrium point leaving zero net hydrogen supply to meet the hydrogendemand.

It is desirable that the present invention provides a hydrogen storagesystem or supply arrangement which addresses one or more of the aboveproblems.

Reference to any prior art in the specification is not, and should notbe taken as, an acknowledgment or any form of suggestion that this priorart forms part of the common general knowledge in Australia or any otherjurisdiction or that this prior art could reasonably be expected to beascertained, understood and regarded as relevant by a person skilled inthe art.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a system fordischarging hydrogen from one or more hydrogen storage vessels, thehydrogen storage vessel or vessels containing solid hydrogen storagematerial, the system including:

a hydrogen supply line for connecting to a hydrogen demand;

an energy delivery system to provide heat to the hydrogen storagematerial in at least one of the hydrogen storage vessel to desorbhydrogen from the solid hydrogen storage material;

one or more supply connection conduits for connecting the supply line toone or more hydrogen storage vessels; wherein

each supply connection conduit connected to a hydrogen storage vesselhas a backflow prevention device to prevent or limit hydrogen in thesupply line from flowing back into that hydrogen storage vessel when thesolid storage material is no longer desorbing hydrogen at the pressureof the supply line.

In the accordance with all aspects of the invention, preferably, whenthe solid storage material is no longer desorbing hydrogen at thepressure of the supply line, the energy delivery system is deactivatedand no longer provides heat to the hydrogen storage vessel.

In preferred forms of the invention the backflow prevention device is aone-way valve or may simply be a shut-off valve. The provision of thebackflow prevention device prevents hydrogen in the hydrogen supply linefrom re-entering an emptied hydrogen storage vessel in which asubstantial proportion of the hydrogen has been desorbed from thehydrogen storage unit and the energy delivery system deactivated orallows the hydrogen to leak back into the exhausted hydrogen storagevessel at an intended low leakage rate. Thus, as the temperature of thehydrogen storage material drops and the hydrogen storage reactionproceeds in the direction of absorbing hydrogen, hydrogen in thehydrogen supply line is prevented from re-entering or only a limitedamount allowed to re-enter the emptied hydrogen storage unit from thehydrogen supply line.

As the kinetics driving the absorption of hydrogen into the cooledhydrogen storage material will absorb all of the available hydrogen inthe emptied hydrogen storage unit and create a partial vacuum in thehydrogen storage vessel. In some instances, it may be desirable for thevacuum to develop.

The invention may provide a means to fill the vacuum by either supplyinggases other than hydrogen such as argon, air or nitrogen or providehydrogen to be provided to the cooling material from an auxiliaryhydrogen supply. The gases other than hydrogen may be supplied or airmay be intentionally allowed to leak into the vessels as they cool.

The auxiliary hydrogen supply may be connectible to the respectiveemptied hydrogen storage vessel when the energy delivery system to thehydrogen storage vessel is deactivated or may alternatively be a smallamount of the supplied hydrogen taken off a branch outlet to the supplyand returned to the vessels.

When an auxiliary hydrogen supply is provided, an amount of hydrogen isfed into the emptied hydrogen storage unit to prevent a vacuum beingcreated. At pressures below the operating pressure for desorbinghydrogen, the kinetics for absorbing hydrogen reduces dramatically. Itis preferred that the auxiliary hydrogen supply, supply hydrogen to theemptied hydrogen storage unit to maintain the pressure in the hydrogenstorage vessel at atmospheric or slightly above atmospheric pressure inorder to prevent leaks forming in the hydrogen storage unit and airentering the unit.

As mentioned above, the auxiliary hydrogen supply may be an auxiliaryhydrogen conduit from the supply line to at least the hydrogen storagevessel which has been deactivated. The hydrogen storage conduitpreferably has a pressure control valve to supply hydrogen to thedeactivated hydrogen storage vessel at a pressure lower than thepressure in the supply line and preferably at atmospheric to 2 bara (orslightly above atmospheric pressure). In one embodiment, the pressurecontrol valve is a step down valve. Alternatively, the auxiliaryhydrogen supply may be a secondary hydrogen storage cylinder such as ahydrogen gas cylinder supplying gas at a pressure of between atmosphericand two atmospheres to maintain the pressure in the deactivated hydrogenstorage unit at a pressure positive to atmospheric pressure.

To further limit the amount of hydrogen reabsorbed into the coolingemptied hydrogen storage cylinder, the rate of cooling of the hydrogenstorage material may be increased by improving the cooling of theemptied cylinder by either or both passive or active cooling of thecylinder. Passive cooling may take the form of removing any externalinsulation which may be covering the exterior of the cylinder and activecooling may involve the use of an air blower over the exterior surfaceof the emptied cylinder or the use of a water-cooled jacket.

In another aspect of the invention there is provided a system fordelivering a supply of hydrogen to a hydrogen supply line including:

one or more hydrogen storage vessels containing solid hydrogen storagematerial,

at least one energy delivery system to supply heat to the solid hydrogenstorage material in at least one hydrogen storage vessel, the heat beingsufficient to desorb hydrogen from the solid hydrogen storage material;and

a control system to control the timing of activation of the energydelivery system based on the hydrogen demand in the hydrogen supplyline, the control system being configured to anticipate a time whenhydrogen will need to be supplied from the hydrogen storage vessel tothe hydrogen supply line to meet the hydrogen demand, and activate theenergy delivery system in the hydrogen storage vessel a period of timeprior to the anticipated time to allow the material in the hydrogenstorage vessel to heat to the temperature at which hydrogen can besupplied at the supply pressure of the hydrogen supply line to meet thehydrogen demand in the supply line.

The above invention may be applicable to a single hydrogen storagevessel in having an energy delivery system and control, system. Thecontrol system would monitor the demand and activate the energy deliverysystem in response to variable which indicates that hydrogen from thehydrogen storage vessel will be required to meet the anticipatedhydrogen demand.

However, in a preferred form, the above system includes two or morehydrogen storage vessels containing hydrogen storage material, thecontrol system being configured to anticipate or determine a time whenhydrogen supply from a first hydrogen storage vessels will fall below apredetermined level and activate the energy delivery system in a secondhydrogen storage vessel a predetermined time prior to the anticipated ordetermined time to allow the material in the second hydrogen storagevessel to heat to the temperature at which hydrogen can be supplied atthe supply pressure of the hydrogen supply line to meet the hydrogendemand in the supply line.

In the preferred form of this invention, the control system comprises asensor which monitors a variable of hydrogen supply to the supply lineand a processor which activates the energy delivery system in the nextsequential hydrogen supply vessel when it determines from signals fromthe sensor that the hydrogen supply in the hydrogen storage vesselcurrently connected to the hydrogen supply line has fallen below apredetermined level.

In another aspect of the invention there is provided a method ofsupplying hydrogen from a hydrogen delivery system to a hydrogen supplyline, the system including one or more hydrogen storage vesselscontaining solid hydrogen storage material, at least one energy deliverysystem to supply heat to the solid hydrogen storage material in at leastone hydrogen storage vessel, the heat being sufficient to desorbhydrogen from the solid hydrogen storage material; and a control systemto control the timing of activation of the energy delivery system basedon the hydrogen demand in the hydrogen supply line.

The method includes the steps of anticipating or determining a time whenhydrogen will need to be supplied from the hydrogen storage vessel tothe hydrogen supply line to meet the hydrogen demand, and activating theenergy delivery system in the hydrogen storage vessel a period of timeprior to the anticipated time to allow the material in the hydrogenstorage vessel to heat to the temperature at which hydrogen can besupplied at the supply pressure of the hydrogen supply line to meet thehydrogen demand in the supply line.

As used herein, except where the context requires otherwise, the term“comprise” and variations of the term, such as “comprising”, “comprises”and “comprised”, are not intended to exclude further additives,components, integers or steps.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIG. 1 is a graph of a typical reaction rate versus temperature curvefor hydrogen absorption of a metal hydride material. The equilibriumpoints between absorption and desorption for a given pressure is definedby the intersection of the x-axis;

FIG. 2 is a flow chart for sequential desorption of manifolded metalhydride cylinders based on digital mass flow meter integration;

FIG. 3 is a flow chart for sequential desorption of manifolded metalhydride cylinders based on heater power integration;

FIG. 4 is a process and instrumentation diagram showing configuration ofpassive gas valves;

FIG. 5 is a FEA simulation of temperature profile of a cylinder coolingunder 1.1 bara.; and

FIG. 6 is a FEA simulation of concentration profile of a cylindercooling under 1.1 bara.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 4, the connection of hydrogen storage vessels 1A, 1B,1C is schematically shown. The hydrogen storage vessels are filled witha suitable hydrogen storage material such as MgH₂ or other hydrideforming alloy which absorbs hydrogen above a predetermined temperatureand pressure and desorbs hydrogen when the temperature is raised abovethe desorption temperature. The vessels are connected in parallel by acommon desorption gas manifold 2 to a hydrogen supply line 3. The supplyline 3 is generally on site where the hydrogen storage vessels aredelivered to meet a hydrogen demand at the site.

A hydrogen conduit 4A, 4B, 4C is connectable to the hydrogen storagevessels IA, IB, IC respectively to receive hydrogen gas discharged fromthat vessel. A hydrogen storage vessel containing hydrogen storagematerial such as magnesium hydride discharge hydrogen under a constantpressure when heated to the absorption temperature. Hydrogen continuesto be discharged until it is substantially empty at which time thedischarge pressure drops dramatically.

The hydrogen discharge conduits 4A, 4B, 4C connecting to the hydrogendesorption manifold are preferably provided with backflow preventiondevices 5A, 5B, 5C such as one way valves which prevent hydrogen gas inthe manifold from returning to the discharge/spent/depleted hydrogenstorage vessel 1A, 1B, IC respectively. As the decrease in dischargepressure from the hydrogen storage vessel occurs close to the point atwhich the hydrogen storage vessel is totally depleted, it is essentialfor the continual supply of hydrogen to the hydrogen supply line thatthe next hydrogen storage vessel to supply hydrogen is heated to therequired desorption temperature by the time that the pressure begins todecrease in the nearly depleted hydrogen storage vessel.

A process controller 7 monitors the desorption process in thedischarging hydrogen storage vessel and commences heating the nexthydrogen storage vessel at an appropriate time prior to the pressuredrop to ensure continuity of supply. This is done by activating heatingelement 6A, 6B, 6C at the appropriate time. The operation of thecontroller will be described in more detail later. The heating elementsmay be electrical heating elements which are located either internallyor externally of the hydrogen storage vessels. To enhance the effects ofthe heating an insulated heating jacket may be provided during theheating and desorption operation. Once the hydrogen storage vessel 1A,1B, 1C has finished discharging hydrogen, the energy source to theheating element of the hydrogen storage vessel is deactivated and thehydrogen storage material is allowed to cool. Ideally any insulatedjacket may be removed when the heating elements deactivated. Asillustrated in FIG. 1, once the hydrogen storage material cools belowthe equilibrium temperature (in the direction of arrow T), the kineticsfor the absorption/the absorption reaction favours absorption ofhydrogen. Hence all hydrogen available to the hydrogen storage materialis absorbed potentially creating a negative pressure (ie. pressure belowatmospheric, 1 bar absolute) in the hydrogen storage vessel.

If it is desirable to prevent pressure in the hydrogen storage vesseldropping below atmospheric pressure, an ancillary supply sourcecommunicates with the exhausted hydrogen storage vessel at least duringcooling. The ancillary supply source may be provided to the supplyconduit 8A, 8B, 8C through a backflow prevention device 9A, 9B, 9C suchas a one way valve. The ancillary supply source may be a separatehydrogen supply 11 such as a gas cylinder through a valve 12 or it maybe a branch line 8 from the absorption gas manifold. The branch line 8is provided with a pressure control valve to step down the pressure fromthe absorption manifold supply pressure to a pressure that is slightlyabove atmospheric ie. preferably in the range of 1-2 bar absolute. Whilethe absorption/desorption reaction is in absorption cycle during thecool down stage of the hydrogen storage material, the reaction kineticsis very slow at that pressure so only a small volume of the hydrogen isactually absorbed.

It may be acceptable to allow a vacuum to develop in the hydrogenstorage vessel and so no ancillary source need be provided.Alternatively the vacuum may be filled with other gases such as argon,nitrogen or air supplied separately or air may be intentionally allowedto leak in and fill the vacuum.

To further limit the amount of hydrogen reabsorbed into the coolingemptied hydrogen storage cylinder, the rate of cooling of the hydrogenstorage material may be increased by improving the cooling of theemptied cylinder by either or both passive or active cooling of thecylinder and as shown in FIG. 1 reduce the reaction rate of the hydrogenabsorbing onto the hydrogen storage material. Passive cooling may takethe form of removing any external insulation which may be covering theexterior of the cylinder and active cooling may involve the use of anair blower over the exterior surface of the emptied cylinder or the useof a water-cooled jacket

The operation of the process controller will now be described. Theindividual control and sequential desorption of each pressure cylinderminimises heat loss by ensuring only one cylinder is actively desorbing.An additional cylinder is pre-heated at an appropriate time toseamlessly take over the supply of hydrogen once the active cylinderempties. The remaining cylinders are stored at room temperature untilrequired

The operation of the system can be simplified as follows

-   -   1. Cylinder A desorbing    -   2. Cylinder A reaches 80% depth of discharge and initiates        warm-up of Cylinder B (taking 15 minutes)    -   3. Cylinder B begins desorbing automatically as soon as it        reaches temperature. At this stage cylinder A is still not 100%        empty. Cylinder A continues to desorb slowly in parallel with        Cylinder B.    -   4. Cylinder B reaches 20% depth of discharge and initiates        cool-down of cylinder A.

Therefore, at any point in time the number of hot cylinders is given asfollows.

Assuming a constant flow rate of hydrogen, the average number ofcylinders heated at any point of time can be estimated as,

avg(n)=1.4

The sequencer controller keeps track of the volume of hydrogen desorbedfrom each cylinder in order to manage the pre-heating of the nextcylinder in the sequence and the cool down of the emptied cylinder. Thesequencer controller can be a programmable logic controller (PLC), apersonal computer (PC), or any microprocessor based embedded controllerwith communications capabilities. FIG. 2 depicts an example softwareflow chart for implementation in a PLC to manage the sequencing of thecylinders.

The depth of discharge can be calculated from integration of mass flowand implemented as shown in FIG. 2. Alternatively, the heater power canalso be used to approximate the mass flow of hydrogen and hence inferthe depth of discharge.

The flow rate of hydrogen is related to the heater power by thefollowing equation,

${F.R.\left( \frac{kg}{h} \right)} = \frac{{P_{heater}({kW})} - {P_{losses}({kW})}}{\Delta \; {H\left( \frac{kWh}{kg} \right)}}$

The enthalpy of reaction ΔH is a chemical property of the hydride. ForMgH₂,

${\Delta \; H} = {10.39\left( \frac{kWh}{kg} \right)}$

The depth of discharge can easily be calculated from the flow rate bysubtracting the integral from the capacity of the storage unit.

${{DOD}(\%)} = {\frac{C_{m\; {{ax}{({kg})}}} - {\int{{F.R.\left( \frac{kg}{h} \right)}{{t(h)}}}}}{C_{m\; {{ax}{({kg})}}}} \times 100(\%)}$

In order for this to be accurate, a good estimate of the instantaneouslosses is needed. The losses will be a characteristic of the storagesystem but will also be dependent on ambient temperature. One possibleway to estimate the losses is by sampling the ambient temperature.Alternatively, the warm-up time of the cylinders will be a function ofthe losses and may also be used.

FIG. 3 depicts an example software flow chart for implementation in aPLC to manage the sequencing of the cylinders based on heater energy.

Alternatively the depth of discharge can be approximated throughobservation of the metal hydride temperature and desorption pressure.

As mentioned above, the cooling down of the solid state cylinders ismanaged by the inclusion of two one way gas valves (9A, 9B, 9C, 5A, 5B,5C) on each cylinder and a pressure control valve between the desorptionmanifold and the absorption manifold.

-   -   The one-way valve on the desorption side of the cylinder        provides an isolation means between the cooling cylinder and the        desorption manifold. So, if cylinder 1A is cooling, hydrogen        cannot flow backwards from the common desorption manifold 2 to        the cylinder 1A. Hence, the cylinder cannot re-absorb hydrogen        that is being sourced from cylinder 1B. However, cylinder 1A can        still induce a vacuum by absorbing all the free gas available        within the cylinder itself.    -   To maintain cylinder 1A under positive pressure, the pressure        control valve 13 between the desorption manifold and the        absorption manifold was added. Where hydrogen is to provide the        positive pressure, the valve feeds hydrogen from the desorption        manifold back into the cylinder at a pressure very close to        atmospheric, e.g. 1.1 bara. The absorption rate at this pressure        for the cooling cylinder is approximately zero and therefore        only a negligible amount of hydrogen is re-absorbed during the        cooling. Once the material is cooled to room temperature the        absorption rate is zero.    -   It may be acceptable to allow cylinder 1A to develop a vacuum        and so no hydrogen would be provided or to use another gas        source such as argon, nitrogen or air to balance the pressure in        the cylinder created by the cooling storage material.

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or drawings.All of these different combinations constitute various alternativeaspects of the invention.

1. A system for discharging hydrogen from one or more hydrogen storagevessels, the hydrogen storage vessel or vessels containing solidhydrogen storage material, the system including; a hydrogen supply linefor connecting to a hydrogen demand; an energy delivery system toprovide heat to the hydrogen storage material in at least one of thehydrogen storage vessels to desorb hydrogen from the solid hydrogenstorage material; a process control system; wherein the process controlsystem monitors the desorption process from the one or more hydrogenstorage vessels; wherein the process control system regulates thedelivery energy from the energy delivery system to the one or morehydrogen storage vessels; one or more supply connection conduits forconnecting the supply line to the one or more hydrogen storage vessels;wherein each supply connection conduit connected to a hydrogen storagevessel has a backflow prevention device to prevent or limit hydrogen inthe supply line from flowing back into that hydrogen storage vessel whenthe solid storage material is no longer desorbing hydrogen at thepressure of the supply line.
 2. The system of claim 1 wherein the energydelivery system is deactivated and no longer provides heat to thehydrogen storage vessel when the solid storage materiel is no longerdesorbing hydrogen at the pressure of the supply line.
 3. The system ofclaim 1 wherein the backflow prevention device is a one-way valve or ashut-off valve.
 4. The system of claim 2 wherein an auxiliary hydrogensupply system is provided to supply hydrogen to the hydrogen storagevessel once the energy delivery system has been deactivated.
 5. Thesystem of claim 4 wherein the auxiliary hydrogen supply system is anauxiliary hydrogen conduit from the supply line to at least the hydrogenstorage vessel which has been deactivated.
 6. The system of claim 5wherein the auxiliary hydrogen conduit has a pressure control valve tosupply hydrogen to the deactivated hydrogen storage vessel at a pressurelower than the pressure in the supply line.
 7. The system of claim 6wherein the pressure control valve supplies hydrogen to the deactivatedhydrogen storage vessel at a pressure slightly above atmosphericpressure.
 8. The system of claim 7 wherein the pressure control valve isa step down valve.
 9. The system of claim 4 wherein the auxiliaryhydrogen supply system is a secondary hydrogen storage cylinder.
 10. Thesystem of claim 9 wherein the hydrogen gas cylinder supplies gas at apressure to maintain the pressure in the deactivated hydrogen storageunit at a pressure positive to atmospheric pressure.
 11. A system fordelivering a supply of hydrogen to a hydrogen supply line including: oneor more hydrogen storage vessels containing solid hydrogen storagematerial, at least one energy delivery system to supply heat to thesolid hydrogen storage material in at least one hydrogen storage vessel,the heat being sufficient to desorb hydrogen from the solid hydrogenstorage material; and a control system to control the timing ofactivation of the energy delivery system based on the hydrogen demand inthe hydrogen supply line, the control system being configured toanticipate or determine a time when hydrogen will need to be suppliedfrom the hydrogen storage vessel to the hydrogen supply line to meet thehydrogen demand, and activate the energy delivery system in the hydrogenstorage vessel a period of time prior to the anticipated time to allowthe material in the hydrogen storage vessel to heat to the temperatureat which hydrogen can be supplied at the supply pressure of the hydrogensupply line to meet the hydrogen demand in the supply line.
 12. Thesystem of claim 11 including two or more hydrogen storage vesselscontaining hydrogen storage materiel, the control system beingconfigured to anticipate or determine a time when hydrogen supply from afirst hydrogen storage vessel will fall below a predetermined level andactivate the energy delivery system in a second hydrogen storage vessela predetermined time prior to the anticipated or determined time toallow the material in the second hydrogen storage vessel to heat to thetemperature at which hydrogen can be supplied at the supply pressure ofthe hydrogen supply line to meet the hydrogen demand in the supply line.13. The system of claim 11, wherein the control system comprises asensor which monitors a variable of hydrogen supply to the supply line,and a processor which activates the energy delivery system in thehydrogen storage vessel when it determines that the hydrogen supply hasfallen below a predetermined level.
 14. The system of claim 13 whereinthe processor deactivates the energy delivery system of one or more ofthe hydrogen storage vessels when the pressure of hydrogen has fallenbelow the pressure in the hydrogen supply line.
 15. A method ofsupplying hydrogen from a hydrogen delivery system to a hydrogen supplyline the system including one or more hydrogen storage vesselscontaining solid hydrogen storage material, at least one energy deliverysystem to supply heat to the solid hydrogen storage material in at leastone hydrogen storage vessel, the heat being sufficient to desorbhydrogen from the solid hydrogen storage material, and a control systemto control the timing of activation of the energy delivery system basedon the hydrogen demand in the hydrogen supply line, the method includingthe steps of anticipating or determining a time when hydrogen will needto be supplied from the hydrogen storage vessel to the hydrogen supplyline to meet the hydrogen demand, and activating the energy deliverysystem in the hydrogen storage vessel a period of time prior to theanticipated time to allow the material in the hydrogen storage vessel toheat to the temperature at which hydrogen can be supplied at the supplypressure of the hydrogen supply line to meet the hydrogen demand in thesupply line.
 16. The method of claim 15 further including the step ofdeactivating the energy delivery system and no longer providing heat tothe hydrogen storage vessel when the solid storage material in thehydrogen storage vessel is no longer desorbing hydrogen at the pressureof the supply line.